The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Wind turbine technology and in particular offshore wind turbine technology is a rapidly developing field of technology. At offshore locations higher wind speeds are available and installation of larger size wind turbines are possible when compared with the onshore systems. The installation and operations of such wind parks provide some technological challenges. The wind turbines are floating or installed on a submarine foundation and are electrically interconnected with submarine power transmission lines. Moreover, such wind parks are typically installed in relatively remote areas, hence the control system of the wind farm and/or the control system in each wind turbine of the wind farm should be able to take measure when problems occur during operation.
One of the problems faced in wind farm operations relates to so-called islanding. Islanding is a situation which may occur if the wind farm or part of the wind turbines of the wind farm becomes disconnected from the electrical grid, e.g. because of planned switching action or protective switching of a circuit breaker in the grid. For example after detection of a power failure circuit breakers may automatically disconnect one or more turbines from the grid. Thereafter, each disconnected wind turbine sets itself to a parking or standby state by stopping rotation of the blades and by pitching the blades. The standby state will last until the islanded wind farm can be reconnected to the grid. During this state, the wind turbine controller and other turbine components, e.g. the environmental controller which controls the environmental parameters (temperature, humidity, etc.) of the wind turbine installation to stay within the requested limits, may be supplied with power from an auxiliary power source.
A conventional wind farm turbine typically uses an uninterruptible power supply (comprising e.g. a battery system, super capacitors and/or a diesel generator set) as the auxiliary power source. Diesel generators however require maintenance and refueling and are thus less suitable for use in offshore and/or remote wind farm systems. Moreover, batteries are sensitive to temperature changes and—in order to ensure a power supply over a long duration—typically a large number of batteries is required. Hence, there is a need in the prior art for improved standby operation of a group of islanded wind turbines.